This project proposes to investigate blood-retinal barrier changes in the retinal pigment epithelium (RPE), Bruch's membrane and the choroid in Royal College of Surgeons (RCS) dystrophic rats, spontaneously diabetic Bio-Breeding (BB) rats, and donor eyes from diabetic humans. Intracellular transport of large molecular weight substances by dystrophic and diabetic cells will be compared to that in normal RPE cells. RCS and BB rats at different ages will be injected intravenously with cationic or anionic isoenzymes of horseradish peroxidase and uptake and intracellular routes of the tracer will be analyzed with the electron microscope. Possible changes in permeability through Bruch's membrane and the choriocapillaris during retinopathy in BB and RCS rats will be studied using the neutral protein, hemoglobin, as an electron microscope tracer. The luminal surface of the choriocapillaris endothelium will be studied in BB and RCS rats using cationic and native ferritin electron microscope techniques in order to determine the role of differentially distributed luminal surface anionic sites in the modulation of transendothelial permeability in the normal eye and during retinopathy. Freeze-fracture, filipin binding and cholera toxin binding techniques will be used to study possible alterations in the distribution of membrane cholesterol and gycolipids which could contribute to a defect in plasma membrane permeability in the RPE of BB rats and diabetic humans. Rapid freeze, deep etch electron microscope techniques will be used to study RPE-Bruch's membrane attachments in diabetic humans and BB rats. The long-term objectives of this research are to determine the basic mechanisms of blood-retinal barrier changes and the relationship of such changes to retinopathy. It is anticipated that such data will contribute to the prevention of and/or treatment of blood-retinal barrier pathology.